We studied the effects of ultralow doses of antibodies to erythropoietin on antenatal and postnatal development of rat offspring. Daily administration of the preparation on days 1-6, 6-16, and 16-19 of pregnancy did not increase embryonic mortality and was not associated with congenital malformations, fetal growth retardation, high incidence of pathological changes in fetal organs, and delayed ossification (compared to control and intact animals). For evaluation of their embryotoxic effect manifested in the postnatal period ultralow doses of antibodies to erythropoietin were administered throughout pregnancy. The offspring of treated and intact rats did not differ in physical development, appearance of sensory and locomotor reflexes, locomotor, exploratory, and emotional behavior, and learning and adaptive capacities.